The present invention concerns a procedure for improving the efficiency of a steam power plant process, in the process damp fuel is used which is dried by conducting at least part of the flue gas flow to dry the fuel.
Through the application DE No.-3 111 011 is known a procedure applied in a steam power plant process, in which preheating of the combustion air is effected with a calorifier. Cooling of the flue gases is effected with a flue gas air preheater (extra economizer). The aim of the procedure disclosed in this reference is to achieve good protection of the flue gas air preheaters (12) against sulphuric acid corrosion. The efficiency of the power plant process cannot be significantly increased with the apparatus design of the reference. No possibilities of control for controlling the ultimate flue gas temperature are disclosed in the reference. On the other hand no need of such control exists in the process described in the reference.
In the application DE No.-2 243 380 a power plant process is disclosed in which preheating of the combustion air is with the aid of water circulation, the feed water going to the water circulation being preheated with tapped steam. Moreover, flue gas cooling has been implemented with a partial feed water flow in this process. The aim in the process of the reference is primarily to separate the air and flue gas passages as regards lay-out. No significant improvement of the efficiency of the power plant process is achieved in the process of the reference. The reference also fails to disclose any so-called flue-gas air preheater ("Luvo"), i.e., a means in which the thermal energy carried by the flue gases is used to preheat the combustion air for the fuel of the boiler.
It is thus known in the prior art, and also through the references cited above, to improve the efficiency of a steam process by heating the feed water with steam tapped from the turbine. It is also known, though perhaps not as common, that preheating of the combustion air is also performed with tapped steam.